|
Deciduous fruit crops such as pipfruit and summerfruit rely heavily on stored nutrients to kickstart next year's growth in the spring.
Nitrogen is by far the most important and the one required in the greatest amounts. There is good scientific evidence to show that trees short in nitrogen reserves give poorer bud break, have poor fruit set and suffer more problems with biennial bearing.
Once the crop is removed, the main root growth flush of the year occurs. This root activity is extremely important for building nutrient reserves for next season. An adequate supply of readily available nutrients in the soil is essential. It is also necessary that soil moisture levels be sufficient for satisfactory root growth. Immediately after harvest a third to half of the annual nitrogen fertilizer requirement should be applied. This year, there has been abnormally high rainfall in some east coast north island districts. On lighter, low fertility soils nitrogen reserves could be lower than normal due to leaching losses, making autumn fertilizer dressings more critical this year than normal. During drought, readily available nitrogen tends to build up in the soil because little is lost through leaching. It has been abnormally dry in some south island and southern north island districts. Here, post harvest irrigation to mobilize root growth and enable uptake will be more important than applying more fertilizer to dry soil.
Potassium tends to compete with calcium and magnesium for uptake. As the autumn root growth flush is important for calcium uptake and potassium is very readily taken up when crop demand for it occurs in the late spring/early summer, the application of potassium, where it is needed, is best left until the spring.
Trees which have had a heavy crop may benefit from post harvest foliar nutrient sprays. Again, nitrogen, usually in the form of urea, should be the key ingredient of these sprays. Among trace elements this is a key time to apply boron.
Manganese and probably zinc are not translocated out of leaves before leaf fall, so post harvest pre-leaf fall foliar sprays of these trace elements are of doubtful value.
| 
